Sea urchin homeo box-containing genes will be studied by molecular cloning and DNA nucleotide sequencing of both genomic DNA and cDNA. The initial selection of the genomic DNA clones will be based on their homology to Drosophila homeo box probes. These sequences and the amino acid sequences they encode will be compared to sequences from other species to infer evolutionary relationships; it will also be determined whether the cloned genes are linked. The genomic DNA and cDNA sequences will be compared to elucidate the structure of the transcription units. The activity of the transcription units in sea urchin oocytes, eggs, embryos and adult tissues will be investigated by probing RNA gel transfers with the cloned sequences. The transcripts will be localized in tissue sections of embryos by in situ hybridization. The protein products will be localized in whole embryos by immunofluorescence microscopy using antibody probes. Since sea urchins are distinctly non-segmented, an analysis of these development controlling genes in sea urchins will provide an informative contrast to the data from the other organisms currently under study and may establish a better understanding of the more general functions of homeo box-containing genes in regulating the transduction of positional information or the determination of cell fate versus the limited function of establishing metamerism. One cannot predict exactly the medical significance of these experiments. When we understand the manner in which genes are regulated, we can hope to use this information to correct any disorders in the process. As the discovery of poly(A) tails has provided a tool for isolating mRNA, so too may the discovery of homeo boxes have provided a tool for isolating genes which regulate the expression of other genes. Further development of in vivo and in vitro systems for studying gene expression and an examination of the effects on these systems caused by normal or mutated homeo box-containing gene protein products may one day make it possible to correct human developmental disorders. The regulation of gene expression is also a central problem in cancer biology.